1. Field of the Invention
This invention relates to an ophthalmological measurement apparatus, and more particularly to an ophthalmological measurement apparatus which irradiates the interior of a patient's eye with a beam of laser light and uses the laser beam scattered from the interior of the eye to output measurement quantities such as the protein concentration in the oculi anterior.
2. Description of the Prior Art
Measurement of protein concentration in the oculi anterior is of considerable importance in determining whether the camera oculi is inflamed, that is, whether the blood-aqueous barrier function is normal or not. In one method that is frequently used for this, a slit lamp microscope is employed to grade the concentration by observation with the naked eye.
Data obtained with the conventional method of naked-eye measurement lacks reliability as judgments vary depending on the person making the measurement. One solution has been to use a method in which a beam of laser light is projected into the eye and the light scattering from the eye is detected and subjected to quantitative analysis.
This method is disclosed, for example, in Japanese Patent Public Disclosures Nos. 120834/87 (corresponding to U.S. Pat. No. 4,957,360) and 135128/88 (corresponding to U.S. Pat. No. 4,832,043). In an ophthalmological measurement apparatus which employs this method of irradiating the eye with a beam of laser light and detecting the light scattered from the eye, the beam from a laser light source is focused on a prescribed point in the eye such as in the oculi anterior, for example, and scattered light from the eye is detected, via a mask with a rectangular aperture of a prescribed size, by a photosensor which converts the light to an electrical signal which is processed to determine the protein concentration in the oculi anterior or other such ophthalmological measurement quantities.
As the photosensor for detecting the scattered light in the aforesaid conventional ophthalmological measurement apparatus there is used a photomultiplier.
Although photomultipliers are adjusted to a prescribed sensitivity at the time of manufacture, the sensitivity tends to vary with the passage of time and the use environment (particularly the temperature). When a photomultiplier is applied for measuring the intensity of scattered light, as in the case where it is used in the measurement of protein concentration in the oculi anterior, such changes in sensitivity lead to measurement error which degrades the measurement accuracy.